if (el.classList) {
  el.classList.toggle(className);
} else {
    var classes = el.className.split(' ');
    var existingIndex = -1;
    for (var i = classes.length; i--;) {
      if (classes[i] === className)
        existingIndex = i;
    }

    if (existingIndex >= 0)
      classes.splice(existingIndex, 1);
    else
      classes.push(className);

  el.className = classes.join(' ');
}
